1. Technical Field
The present invention relates to a device and a process for collecting a sample for analysis to be used for determining the content of impurities in a metal, particularly a solder easily, rapidly and with high accuracy.
2. Description of the Related Art
Previously, as one of methods of connecting an electronic part to a substrate in manufacturing an electronic circuit substrate, a flow soldering method of using a molten solder material in a form of a jet has been known. This flow soldering method includes generally a flux coating step of coating a substrate with a flux, a pre-heating step of heating the substrate in advance, and a solder material supplying step of contacting the substrate with a jet consisting of a solder material to supply the solder material to the substrate. The previous general flow soldering method will be explained with reference to drawings below. FIG. 22 is a schematic cross-sectional view of the previous flow soldering device. FIG. 23 is a cross-sectional view along with a X′-X′ line of FIG. 22.
First, a flux is supplied to a substrate such as a printed board on which electronic parts such as a through-hole insertion part are properly disposed at predetermined positions by the known method, using a flux supplying means (now shown), thereby, an underside of the substrate is coated with a flux. The flux usually contains an active component such as rosin (resin component) and a solvent such as isopropyl alcohol, and such the flux coating step of coating the substrate with the flux is performed for the purpose of removing an oxidized film (natural oxidized film) which is unavoidably formed on a land (i.e. a part to which a solder material is to be supplied) formed on the substrate, thereby, making wetting spreading of a solder material on a land surface better. As the flux supplying means, a spray fuxer for spraying a misty flux to the substrate, or an expansion fluxer for contacting a foamy flux with the substrate can be used. Such the flux supplying means may be constructed separately from a flow soldering apparatus, or may be integrally incorporated into the interior of a flow soldering apparatus 70.
The substrate coated with a flux as described above is supplied to the flow soldering apparatus 70 of FIG. 22 through an inlet part 71. The substrate 81 is mechanically conveyed in the interior of the apparatus 70 (along with a conveyance line shown with a dotted line in FIG. 22) at constant rate in a direction of an arrow 72. More particularly, conveyance of the substrate 81 is performed by mechanically transferring conveyance claws 82a and 82b holding the substrate 81 at their both ends in a conveyance direction of an arrow 72 as shown in FIG. 23. Herein, conveyance claws 82a and 82b are connected to chains 84a and 84b, respectively, and are roated about conveyer frames 83a and 83b extending from the inlet part 71 to an outlet part 79 shown in FIG. 22 in a plane parallel with a main plane of the substrate 81, respectively. The conveyer frame 83a is a fixed conveyer frame on a standard side, and the conveyer frame 83b is a conveyer frame, on a width adjustment side, which can be slided in a direction vertical to a conveyance direction 72, and parallel with the fixed conveyer frame 83a (i.e. to the left and to the right in a paper plane of FIG. 23).
The substrate 81 which is conveyed in the interior of the apparatus 70 from the inlet part 71 to the outlet part 79 like this is first heated with a pre-heater 73 situated below the substrate 81, such as a far infrared-ray heater. This pre-heating step by heating is performed for heating the substrate 81 in advance prior to supply of a solder material 74 to the substrate 81 to decrease a temperature gradient in an upper and lower direction of the substrate to raise a temperature of a substrate body, for vaporizing an unnecessary solvent component in a flux coated on the substrate 81 by the flux coating step, and for shortening a wetting time (a necessary time from contact of a solder material with a material to be connected (a land in this case) to wetting initiation). Generally, as shown in FIG. 23, the pre-heater 73 has an upper end connected to the fixed conveyer frame 83a and a fixed frame 85, is disposed on a bottom of a groove structure (or a support) 86 having an opening at its upper part, and is disposed below a conveyance line of the substrate 81, and heats the substrate 81 from the same side as a side to which the solder material is supplied, that is, from a lower side of the substrate 81, in a subsequent solder material supplying step.
Subsequently, the substrate 81 is conveyed to above a solder material supplying means 76 including a solder tank 75 charged with a solder material 74 which has been molten by heating in advance, and contanted with a primary jet 77 and a secondary jet 78 consisting of the solder material 74 on a side of an underside of the substrate 81, thereby, the solder material 74 is supplied to the substrate 81. Thereupon, the solder material 74 is wetted up by capillary phenomenon from a side of an underside from the substrate, in an annular space between an inner wall of a through-hole (not shown) formed in the substrate 81 and a lead (not shown) of a through-hole insertion part which is inserted into a through-hole from an upper side of the substrate 81. Thereafter, the solder material which has been supplied and adhered to the substrate 81 solidifies by a fall in a temperature, and forms a connection part consisting of a solder material, a so-called “fillet”.
In this solder material supplying step (or flow soldering step), a primary jet 77 is for covering a wall surface of a through-hole to sufficiently wet a surface of a formed land (and a lead of an electronic part) with the solder material and, when this is insufficient, the solder material is not sufficiently wetted up in an annular space between the through-hole and the lead, and a problem of a so-called “land exposure” arises. And, a secondary jet 78 is for removing a solder material adhered to a region covered with a solder resist to adjust a shape of a fillet and, when this is insufficient, the solder material stays and solidifies over lands to form a so-called “bridge” (this bridge is not desirable because it leads to short of an electronic circuit), or forms a square-shaped projection, being not desirable.
The thus obtained substrate 81 is thereafter taken out through the outlet part 79, thereby, an electronic circuit substrate on which electronic parts are soldered to the substrate 81 by the flow soldering method is manufactured.
In the electronic circuit substrate manufactured as described above, previously, a Sn—Pb-based solder material containing Sn and Pb as a main component, particularly a Sn—Pb eutectic solder has been keen generally used. However, since lead contained in a Sn—Pb-based solder material may result in environmental contamination due to improper waste disposal, as a substitute for a solder material containing lead, a solder material containing no lead, a so-called “lead-free solder material” has been started to be used at an industrial scale.
As the “lead-free solder material”, Sn—Cu-based, Sn—Ag—Cu-based, Sn—Ag-based, Sn—Ag—Bi-based, Sn—Ag—Bi—Cu-based, Sn—Sb-based, Sn—Bi-based, Sn—Zn-based, and Sn—Zn—Bi-based materials are started to be studied and put into practice.
As a trend of the world for a lead-free material, particularly in Europe, Directive Concerning Restriction on Certain Hazardous Substances Contained in Electric Electronic Apparatuses(hereinafter, referred to as “RoHS Directive”) is planned to be enforced from July, 2006, and use of lead which is one of four certain hazardous substances(lead, mercury, cadmium, hexavalent chromium) is prohibited. That is, it becomes essential to switch from a Sn—Pb-based solder to a lead-free solder.
Further, since RoHS Directive plans that a limit value of the content of certain hazardous substances is 100 ppm for cadmium, and 1000 ppm for lead, mercury and hexavalent chromium, even in the case of a lead-free solder such as Sn—Cu-based, Sn—Ag—Cu-based, Sn—Ag-based, and Sn—Ag—Bi-based ones, it is necessary to regulate and control the content of certain hazardous chemical substances, particularly lead, which may be mixed therein as impurities.
For impurities contained in a sample of a metal material, the content thereof can be determined by energy dispersive fluorescent X-ray analysis. In energy dispersive fluorescent X-ray analysis, a flat surface of a metal sample having a predetermined area is irradiated with primary X-ray, and a characteristic(fluorescent) X-ray spectrum generated from elements present in, a superficial layer up to a depth of 100 μm from a surface is measured, thereby, components of substances contained in a metal sample, and their contents are analyzed. Energy dispersive fluorescent X-ray analysis has a very high sensitivity, and detects a few hundreds ppm of impurities at a measurement error of around ±10 ppm.
As a general metal sample which is subjected to energy dispersive fluorescent X-ray analysis, a flat plate having a constant thickness and a small surface roughness, which was manufactured by rolling procession, is used. However, in a solder material unlike a general metal material such as a steel material, a plate is not manufactured by rolling procession.
Previously, for producing a solder sample for analysis, a solder sample has been produced by scooping up a molten solder 92 heated in a solder tank 91 with a crucible 94 equipped with a pincher 93, and cooling and solidifying it in the crucible 94 as shown in FIG. 24A. or a solder sample 96 for analysis has been produced by transferring a molten solder from the crucible 94 to a metal plate (for example, see JP-A No. 2000-121514).
In addition, a metal sample for analysis in a metal refining process has been produced by a sample producing device 100 in which a mold 101 with an inlet port 102 is provided at its tip, as shown in FIG. 25. First, the mold 101 at a tip of the sample production device 100 is immersed in a molten metal, to flow the molten metal into the mold 101. The mold 101 into which the molten metal has been flown is taken out from the molten metal into the air, and cooled to cool the molten metal in the mold 101, thereby, a metal sample for analysis is produced (for example, JP-A No. 2004-012336).